The Onset-of-Effect Questionnaire (OEQ) is a self-administered instrument used to assess patient perception of how quickly asthma maintenance medications begin to work. This study was designed to quantify the relative importance that patients using combination inhaled corticosteroid and long-acting beta(2)-agonist (ICS/LABA) maintenance medication place on the onset-of-effect outcomes. Patients aged >or=18 years with a self-reported diagnosis of asthma, currently using combination ICS/LABA maintenance medication, completed an Internet-based SC conjoint survey instrument that included 10 choice trade-off tasks. In four choice tasks, patients were asked to choose between two hypothetical medications. In six choice tasks, patients were asked to choose among two hypothetical medications and their current medication. Each choice alternative was defined by response levels of the five OEQ statements and out-of-pocket cost. We used random-parameters logit methods to estimate the relative importance of outcomes assessed by the OEQ. Five hundred nine patients completed the study. Satisfied was the most important OEQ outcome and physical sensations were the least important. When offered a choice, 80% (95% CI, 75-85%) of patients preferred a maintenance medication for which they are satisfied with how quickly they feel it begins to work and 62% (95% CI: 57-67%) of patients preferred a maintenance medication that they feel begins to work right away. Combination maintenance medications with rapid onset of effect, especially those that impact a patients' ability to feel the medication work right away and patient satisfaction with how quickly the medication works, may increase the use of and adherence to maintenance medications.